Electric discharge device



June 15, 1937. c, K 2,084,163

ELECTRIC DISCHARGE DEVICE Filed March 21, 1936 111 111111, "11","l-llapll";lll,lll

Inventor: Caid H. Peck b His Attorney.

Patented June 15, 1937 UNITED STATES ELECTRIC DISCHARGE DEVICE Caid H. Peck, Schenectady, N. Y., assignor to General Electric Company, a. corporation of New York Application March 21, 1936, Serial No. 70,141

7 Claims.

My invention relates to electric discharge devices adapted to operate in the presence of an ionizable medium, and more particularly to such devices as are operated at a pressure suflicient to support an arc discharge of electrically constricted nature. In general, these comprise rectifiers of the type disclosed in Patent No. 1,266,517, G. S. Meikle, granted May 14, 1918.

For rectifying apparatus in which high emciency is a prime requisite it is frequently desirable to employ electric discharge devices operating in an ionizable atmosphere at a gas pressure on the order of at least 1 centimeter of mercury. While the use of such pressures makes it possible to obtain extremely efficient cathode emission, certain incidental operating conditions are encountered thereby which raise special problems of construction.

One of these conditions arises from the fact that the range of pressure required to yield the desired cathode efficiency causes the discharge to take the form of an electrically constricted are which concentrates on a small area of the anode surface. This concentrated discharge produces unforeseen difliculties in attempting to adapt.

this type of rectifier to the metal enclosing envelopes now recognized as commercially desirable. In particular, the impingement of the concentrated are stream on a restricted area of the relatively thin wall of the metal receptacle, which is commonly used as the anode, produces considerable burning of the same and eventually causes a leak to be developed. Even if an actual breach in the metal is not produced, the extreme localized heating results in the evolution of objectionable foreign gases and produces a slow leak by rendering the metal porous.

In accordance with the present invention I have found that not only the effects but also the actual existence of this undesirable condition may cathode.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing in which Fig. 1 shows in sectional elevation a complete discharge device embodying my invention; Figs. 2,

3, 4, 5, and. 6 illustrate alternative embodiments thereof, and Fig. 7 is a cross-sectional view taken on line 'l--I of Fig. 4.

Referring particularly to Fig. 1, there is shown in the drawing a discharge device comprising a metallic envelope, at least the main surface of which consists of a metal cylinder. In accordance with usual practice this may comprise a section of seamless steel tubing. The cylinder l is closed at the top by a flanged metal header 2 hermetically sealed thereto, as by a continuous weld, and at the bottom by a header 3 secured in similar fashion.

Inside the envelope I provide a cathode 4 which preferably comprises a spiral filament of an electron emissive material, such as thoriated tungsten. Heating current is supplied to the cathode element by means of a pair of lead-in conductors 5 which are passed through air-tight glass-tometal seals 6 provided for that purpose.

For assuring the desired conditions of operation an ionizable medium having the desired pressure is introduced into the metallic envelope prior to sealoif by means of the exhausting tube 1. If the medium employed consists of a vaporizable material, such as mercury, it is desirable to 50 design the dimensions of the envelope that it will operate at such temperature that the vapor pressure of the mercury is maintained at the desired point. This will generally be above about 1 or 2 centimeters of mercury, but for the purposes of this invention may best be defined as a pressure characterized by an electrically constricted arc discharge.

If the operating medium to be utilized consists not of mercury but of an ionizable gas, such as argon, it is necessary to introduce the same at approximately the pressure at which the device is intended to operate. In the case of argon this would be above about 1 or 2 centimeters and, in the case of neon, above at least one-half atmosphere. Here again, however, the figures and materials given are exemplary rather than limiting. Instead of the particular ionizable materials mentioned, it may in some cases be preferable to use a mixture thereof, such as a combination of argon and mercury.

In the use of a discharge device such as that above described it is convenient to use as an anode the wall of the metallic envelope itself, which may be grounded or maintained at a discharge potential with respect to the cathode by suitable connections made through the lug 9. Due to the high gas pressure employed it is possible to apply the cathode heating potential and the anode potential at the same time without encountering destructive bombardment of the oathode surface. Furthermore, the thoriated tungsten filament may be operated at a temperature as high as 2400 Kelvin whereby excellent emission efiiciency may be realized. It has been observed that the high gas pressure prevents deactivation of the cathode from taking place at this temperature, which is substantially in excess of that which might safely be used with lower pressures.

As a further result of the high pressure, the rectifying discharge takes the form of a threadlike are proceeding from the cathode to the nearest point on the envelope surface. This phenomenon of electrical constriction, which is characteristic of the class of devices with which my invention is principally concerned, produces extreme localized heating of the adjacent anode surface upon which it impinges, in this case, the header 2. If this header comprises sheet metal of the thickness usually employed in tube manufacture the heat becomes sumciently intense to cause burning and vaporization of the metal to an extent which rapidly produces a leak in the header wall.

In accordance with my present invention this effect is substantially eliminated by the use of a body or mass of heat conducting material III in contact with the header 2. This mass should be of a metal or other substance having relatively high thermal capacity and conductivity and may take various forms depending upon the circumstances of manufacture. For example, it may comprise a thick slug of copper, aluminum or similar material melted into the cup-like enclosure formed by the header 2. Alternatively one may utilize a thick cylinder of preformed copper affixed by brazing or otherwise in intimate contact with the header wall.

While the dimensional relationships are not critical, I have found that with an envelope of tubing 2 inches in diameter and about .035 inch thick, good results may be obtained by using a copper slug about 4, inch in thickness. If the material employed is of lower heat conductivity, as in the case of iron, the thickness may need to be increased to about inch. In any case, it should be of substantially greater thickness than the sheet metal of the envelope walls.

In the alternative embodiment of Fig. 2, in which corresponding parts are identically numbered, I have shown a mass of heat conducting material ll placed in contact with the inner rather than the outer wall of the header 2. If mercury is to be used as the operating medium for the discharge it will be desirable to form the member ll of iron or some other metal which is not attacked by mercury vapor. I

In this modification, as in that previously described, the resultant increase in the thickness of the anode wall nearest the cathode, results in a sufiicient increase in heat dissipating capacity to prevent burning of the metal. This is presumably due to the enhanced thermal conductivity of the'increased cross-section of metal.

In Fig. 3 I have illustrated the application of my invention to an envelope structure of somewhat different form. In this embodiment the envelope takes the shape of an elongated cylinder l2 terminating in a hemispherical header portion l3 integrally connected therewith. The lower portion of the cylinder is closed by abutment of a header H which is provided with a pair of glass to-metal seals l5. These latter are adapted to receive lead-in conductors It for supplying current to the cathode II. In this case, protection against excessive heating is provided by a slug of metal l8 fused or otherwise secured at the uppermost part of the hemispherical portion II.

In the further embodiment shown in Figs. 4 and 7 the heat-dissipating means takes the form of a thick cylinder of metal 20 arranged concentrically and in tight fitting contact with the inner surface of the envelope 2|. In this arrangement, since the cathode 22 approaches the side walls of the envelope more closely than it does the end. the arc discharge will actually be received by the cylinder 20, which is capable of dissipating the heat thus created.

The devices of Figs. 5 and 6 are similar in principle to the constructions already described and differ therefrom chiefly in utilizing the heat dissipating element itself as a means of completing the envelope closure. In Fig. 5 the thickened iron disk 24 is hermetically sealed at its periphery to the inner surface of the cylinder 25 in close adjacency to the cathode 26. In Fig. 6 a similar disk 21 is welded into sealed contact with an abutting flange 28 provided at one e x-, tremity of the cylinder 29. Here again, the discharge will necessarlly take place directly from the cathode 30 to the inner surface of the disk 21.

The effectiveness of the invention described in the foregoing depends in part upon the fact that the outside of the enclosing envelope is ordinarily exposed to a cooling medium. This will usually be the ambient atmosphere, but may, if desired, comprise an artificial medium such as a blast of air or a current of other cooling fluid. The use of a mass of heat conducting material adjacent the region at which the intense are impinges on the envelope interior surface permits a very rapid diffusion of the heat generated to the adjoining parts. From these it is dissipated into the external medium at a rate sufficient to prevent the occurrence of cumulative localized heating and consequent burning of the metal.

While I have shown particular embodiments of my invention, it will of course be understood that I do not wish to be limited thereto since many other modifications in the structure may be made, and I contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric discharge device including a thermionic cathode, an anode comprising a sealed metallic envelope surrounding said cathode, an ionizable medium therein having during operation of the device a pressure sufilclent to support an electrically constricted arc discharge between the anode and cathode and a mass of material of good thermal conductivity affixed to said envelope in the region of its nearest approach to said cathode.

2. An electric discharge device including a thermionic cathode, an anode comprising a sealed metallic envelope surrounding said cathode, an ionizable medium therein having during operation of the device a pressure sufficient to support an electrically constricted arc discharge between said cathode and a confined region of said envelope and a mass of material of good heat conductivity aflixed to said envelope adjacent said region.

3. An electric discharge device including a thermionic cathode, a sealed envelope enclosing said cathode and having a thin metal wall portion constituting an anode for receiving an All are discharge, an ionizable medium in said envelope having during operation of the device a pressure of at least about one centimeter of mercury, and a mass of material of good heat conductivity afllxed to said envelope wall portion.

4. In an electric discharge device, a thermionic cathode, a metal envelope surrounding said oath ode and having at least a portion of its surface adapted to serve as an anode, an ionizable medium in said envelope having during operation of the device a pressure sufficient to support an electrically constricted arc discharge between the anode and cathode, said portion of the envelope surface including a thick metal body aflixed thereto or forming a part thereof at the region of impingement of said are discharge.

5. An electric discharge device including a thoriated tungsten cathode, an anode comprising a sealed envelope of sheet metal surroundin said cathode, a quantity of mercury in said envelope having during operation of the device a pressure of at least about one centimeter of mercury, and a mass of material of good heat conductivity aflixed to said anode in the region of its nearest approach to said cathode.

6. In an electric discharge device a sheet metal cylindericomprising an envelope for said device, a sheet metal header closing one end of said cylinder, and adapted to serve as an anode, a thermionic cathode adjacent the inner surface of said header, an ionizable medium in said envelope having during operation of the device a. pressure sufllcient to support an electrically constricted arc discharge between the anode and cathode, and a mass of material of good heat conductivity aflixed to said header.

7. An electric discharge device including the combination of a cathode, an envelope enclosing the cathode, said envelope consisting at least partially of a thin metal wall which is maintained at a discharge potential with respect to the cathode during operation of the device, an ionizable medium within the envelope having a suflicient pressure during operation to confine the discharge between the cathode and said metal wall to a constricted are form, and a metal body of substantially greater thickness than the metal wall affixed to such wall at the region of impingement of the constricted arc discharge.

CAID H. PECK. 

